In drilling operations, a surface winch commonly referred to as drawworks is used to hoist a drill string via a cable whereby the drawworks is effective to payout and reel in the cable in order to raise and lower the drill string as desired. The drawworks includes a brake that controls the drill string payout to adjust the pressure applied to the drill bit suspended from the drill string against the earth formation at the bottom of a wellbore. As drilling progresses the pressure or “weight-on-bit” decreases. By releasing the drawworks brake, the weight-on-bit may be applied to the drill bit against the earth formation to promote further drill of the bore hole. Accordingly, the drawworks brake controls the payout of the drill string for affecting drilling parameters such as weight-on-bit and rate of penetration in a wellbore.
On many drilling rigs, the drawworks are equipped with band brakes surrounding the drawworks drum that are mechanically controlled by a driller/operator via a brake lever. Automated systems for controlling the brake lever have also been developed. For example, tension spring/wire line arrangements have been used to manipulate a drawworks brake lever back and forth between a brake position of the band brake and a release position of the band brake. However, tension spring/wire line arrangements must be detached from the brake lever and then re-attached between drilling intervals when making a connection of drill pipe resulting in lost production time. A hydraulic servo control has been developed to manipulate a drawworks brake lever. However, the cost for providing a hydraulic power unit, modifications to the existing drilling rig equipment and the limited intelligence of a hydraulic-mechanical system has resulted in limited application.
It is desirable to provide a means for controlling band brake drawworks unlike the above describe techniques.